The biological effects of radiation are being investigated in connection with radiosensitization and protection at the molecular level relevant to cancer therapy. The inactivation of aqueous enzymes is being studied with pulse radiolysis and steady irradiation techniques, as models of target macromolecules with localized active regions. This work will be extended to metalloenzymes and enzyme-dye complexes to explore the feasibility of controlling the attack of radicals by ligand complexing. A systematic investigation is being carried out on the effects of solute concentration on the radiosensitivity of E. coli bacteriophage for a series of amino acids and sugars, with the objectives of evaluating the role of medium on the extent of direct and indirect action and the corresponding oxygen effects. Protein targets in bacteriophage inactivation are being studied with radical anions that react selectively with amino acid residues. These studies will be extended to micellar and model membrane systems in new work. A major improvement in the pulse radiolysis system is in progress which will make possible programmed data taking and on-line computer analysis of results.